Applicant incorporates by reference herein the contents of Korean patent application No. 92-3389 filed Feb. 29, 1992.
The present invention relates to an automatic focus circuit used in a video camera, and more particularly to an automatic focus circuit for performing automatic focus by evaluating integrated values of digital luminance signals for a divided area on the monitor screen.
There are two basic types of conventional automatic focus apparatus used in a video camera, for example, the infrared ray type and the Honeywell type developed by the Honeywell Company.
Both the infrared ray type automatic focus apparatus and the Honeywell type automatic focus apparatus largely employ a mechanical system except for the electrical circuit, such as a comparator 2 and a controller 1. FIG. 1 is a diagram schematically showing an example of an automatic focus apparatus in accordance with the conventional system.
As shown in FIG. 1, a light emitting device emits infrared rays to an object, and a receiving sensor 5 receives an optical signal from a reflecting prism 4 which receives the optical signal through a fixed mirror 2 and an injection mirror 3. A microcomputer 7 makes a computation utilizing an electrical signal compared in comparing circuit 6 and provides a control signal for automatic focus to an automatic focus motor 8 which is mounted at a lower portion of the body of photographing lens 9.
The conventional automatic focus apparatuses have a complicated constitution and have difficulty in performing automatic focusing.